Sheet metal forming has been used in the industry for years for creating metal parts from a blank sheet metal, for example, automobile manufacturers and their suppliers produce many parts using sheet metal forming. One of the most used sheet metal forming processes is deep drawing, which involves a hydraulic or mechanical press pushing a specially-shaped punch into a matching die with a piece of blank sheet metal in between. Exemplary products made from this process include, but are not limited to, car hood, fender, door, automotive fuel tank, kitchen sink, aluminum can, etc. In some areas of the die, the depth of a part or product being made is generally more than half its diameter. As a result, the blank is stretched and therefore thinned in various locations due to the geometry of the part or product. The part or product is only good when there is no structural defect such as material failure (e.g., cracking, tearing, wrinkling, necking, etc.).
FIG. 1A shows an exemplary deep drawing manufacturing setup, in which a sheet metal blank or blank 120 (i.e., an unformed sheet metal plate before being formed) rests on a blank holder 108 between an upper die 110 and a punch 130. The blank 120 is formed into a sheet metal part when the die 110 is pushed down to the punch 130 in the direction of the draw axis (shown by an arrow 140). The die 110 includes a product design section 102, binder section 106a-b and addendum section 104a-b. A number of guide pins or guide posts 122 are configured for precisely the blank 120. FIG. 1B shows a plan view of an exemplary sheet metal blank 160 and guide pins 162. The sheet metal blank 160 can move laterally within a perimeter defined by locations of the guide pins 162. For illustration simplicity, an oval shape is shown for the sheet metal blank 160. Those of ordinary skill in the art would know that the sheet metal blank 170 can have any arbitrary shape shown in FIG. 1C. The sheet metal blank 170 is surrounded by a number of guide pins 172.
In order to successfully manufacture a sheet metal part, many of the today's manufactures uses computer or numerical simulations (e.g., Computer Aided Engineering Analysis (CAE)) to help them to achieve such a goal. One useful computer simulation is based on finite element analysis (FEA), which is a computerized method widely used in industry to model and solve engineering problems relating to complex systems. FEA derives its name from the manner in which the geometry of the object under consideration is specified. With the advent of the modern digital computer, FEA has been implemented as FEA software. FEA software can be classified into two general types, implicit FEA software and explicit FEA software. Implicit FEA software uses an implicit equation solver to solve a system of coupled linear equations. Such software is generally used to simulate static or quasi-static problems. Explicit FEA software does not solve coupled equations but explicitly solves for each unknown assuming them uncoupled. Explicit FEA software usually uses central difference time integration which requires very small time steps for the method to be stable and accurate. Explicit FEA software is generally used to simulate short duration events where dynamics are important such as impact type events.
In simulating a deep drawing manufacturing of a sheet metal part, a number of different types of simulation are performed. FIG. 2 lists an exemplary series of such simulations. The exemplary series is a metal forming simulation (e.g., forming an automobile part from sheet metal). Metal forming simulation comprises a number of phases: 1) gravity loading 202, 2) binder wrapping 204, 3) punch lowering 206, 4) binder release for springback 208 and 5) edge flanging and hemming 210.
The present invention is directed to numerically simulation of the gravity loading phase 202 of a deep drawing manufacturing. In particular, effects of guide pins in contact with sheet metal blank are considered and modeled in the simulation. During gravity loading phase, the sheet metal blank 120 is placed on top of the blank holder 108. The sheet metal blank 120 can move laterally without constraint until it contacts with one or more guide pins 122.
Prior art approaches have been requiring drastic changes to the computerized model (i.e., refining FEA mesh) of the sheet metal blank so that contacts between the sheet metal blank and guide pins can be detected. Drawbacks for refining FEA mesh of the sheet metal blank are not only tedious, but also expensive in terms of man hours and computer resources (i.e., larger memory, longer execution time, etc.).
It would therefore desirable to have more efficient systems and methods in gravity loading phase of a deep draw manufacturing simulation including effects of sheet metal blank in contact with guide pins.